Really? perhaps you should just try to find & ride your first train without getting killed. Then if you dont die, repeat.
I like the idea of a lanyard but I dont know how blind you are without your cheaters. It seems that you are really fucking blind or just cautious & thinking ahead.
Perhaps you can invest in some sports glasses like the wear for basketball.
I would just rock what you got & try to protect them. I have seen kids bail from trains & bust up their glasses & have to tape them together. I dont wear eyeglasses. Perhaps you can carry 2 pairs? You can put the nice ones in a hard case & wear your backups while hopping trains.
If you ever get State sponsored medicaid for being low income, that may be a good way to get more free glasses that fit you with your exact prescription.
I know the lions clubs collects used glasses & then distributes them to the needy. Often they will have a cardboard box just collecting them at a mall or supermarket. Im sure you could dig through the box & grab pair & or just reach out to a lions club where ever you are.
http://www.lionsclubs.org/EN/how-we-serve/health/sight/eyeglass-recycling.php